1. Field of the Invention
This invention relates to an apparatus and a method for adjusting clock signals, and more particularly, to a self-adjusting apparatus and a self-adjusting method for adjusting an internal oscillating clock signal by using the self-adjusting apparatus.
2. Description of Related Art
A clock generator is normally included in the design of an electronic circuit for generating clock signals to control the sequence of signal and data processing and to synchronize different signals in order to prevent the occurrence of malfunction caused by disordered signal processing sequence. In most electronic circuits, the clock signal generated by a clock generator is often used as a trigger for activating a process and resetting a process. In some situations, the clock signals also serve as a reference signal.
According to the current designing demand, a clock generator has become a required component of an electronic circuit that includes integrated circuits (ICs), so that the ICs can operate in various power-consuming modes, such as normal mode and power-down mode, depending on the actual needs for energy-saving purposes. Conventionally, a clock generator includes a crystal and an oscillator. It is designed to be external to an IC, and to be connected to the IC by an electronic circuit. However, since the power supply to the clock generator is independent from that to the IC, the power distribution of the electronic circuit becomes more complicated. Furthermore, the power supply to the clock generator alone has become a drain of system power even while the IC is running in a power-down mode.
Another conventional design of an electronic circuit including an IC and a clock generator forms the clock generator inside the IC in order to make the device more energy-conservative. The built-in clock generator is normally formed by implementing a logic device fabrication process into the fabrication process of the IC. However, the clock generator made with a logic device fabrication process alone can hardly provide a very precise internal clock signal; therefore, some extra processes are required to ensure that the clock signal generating frequency is acceptable. In addition, the clock generator is non-adjustable once it is made. As a result, the IC is useless if the built-in clock generator cannot generate a clock signal in a precise frequency.
In view of the foregoing, there is a need for a self-adjusting apparatus and method that is able to adjust the internal oscillating clock signal while the device is running in a normal mode accordingly to an external clock signal.